


Nightmarish Heat

by xXUndertale_loverXx



Series: Collabs [3]
Category: Undertale
Genre: Begging, Comfort, Crying, Cuddling, Desperate, Dom Cross, Ecto-Vagina, Ecto-dick, Fear, M/M, Masturbating, Oral, Passive Nightmare, Sentient Tentacles, Skeleton Heat, Sub Nightmare, ecto-pussy, heat - Freeform
Language: English
Status: Completed
Published: 2018-06-06
Updated: 2018-06-06
Packaged: 2019-05-18 23:10:04
Rating: Explicit
Warnings: Creator Chose Not To Use Archive Warnings
Chapters: 1
Words: 3,591
Publisher: archiveofourown.org
Story URL: https://archiveofourown.org/works/14862077
Author URL: https://archiveofourown.org/users/xXUndertale_loverXx/pseuds/xXUndertale_loverXx
Summary: Nightmare has gone through heat and his tentacles are out of control. Because of his tentacles' refusal to follow his orders anymore, they do whatever they want- which in his case stimulating him with teasing suggestive touches. Being out of his dark form because of his tentacles' sudden intelligence, it leaves him vulnerable and weak. Two things he hated. Additing salt to the wound, Cross walks in on his most vulnerable moment and he won't leave. Fantastic.But maybe he can actually enjoy his heat for once.-Roleplay style-





	Nightmarish Heat

**Author's Note:**

> ### This story is by me (X) and SkylerSkyhigh.
> 
> Sky:   
> I saw a pic about NaJ Nightmare in heat and oh boy that was hot. And it gave me an idea to make Nightmare subjected under the mercy of his own tentacles. Of course the idea expanded to someone walking in on him and helping him with his heat. Talked to X about it and this happened. Enjoy this fic!
> 
> Me - Nightmare  
> X - Cross/Tentacles

Nightmare moaned loudly as a shudder wracked through his entire frame. He's being cradled by his tentacles in his room. The black tendrils stimulating him and touching him in ways that made him shiver with need. He hated that it felt so good.

Stupid heat. Stupid tentacles. Stupid corrupted goop!

~~~

His tentacles writhed around him, touching all his sensitive spots but never once got close to his pelvis where Nightmare needed the stimulation. They curled around his ribs, around his spine and stroked the insides of his thighs.

~~~

"Ngh-!" Nightmare cut off a moan that wanted to escape by biting his lip, curling into himself slightly. He panted hard with need, his pussy already formed a long while ago. The magic throbbing and aching terribly.

Why is he always so weak during his heat? Why did his goop suddenly have it's own mind during his heats?! Now with the goop off his body, the normally black bones snow an ivory white. The bones sensitive to every touch and the tendrils used that to their advantage. He struggled lightly against the tentacles. He hated his heats. 

~~~

One tentacle slid dangerously close to his pussy, rubbing along the magic slightly, never once touching his lips.

A thick tentacle wrapped around his spine and squeezed gently, sliding over it.

~~~

Nightmare's breathing stuttered as the tendrils slid teasingly close to his throbbing mound. He's practically dripping onto the tentacles supporting his pelvis but that one held him still. He couldn't move and fuck himself on the tentacles that seemed to have a mind of his own during his heats.

Nightmare arched his back with a moan when it touched his spine. "Aahh~! Please! Just...touch me already!" he screamed, tears dotting the corners of his eyes.

~~~

The tentacle rubbed slightly lower but just when it was about to touch his pussy it withdrew completely.

The tentacle on his spine gently pumped his spine, rubbing against the sensitive vertebrae.

~~~

Nightmare writhed against the tentacles as he was teased again, moaning softly while panting. His face covered in a purple blush as his eye lights went fuzzy.

"Just-! Fucking stop teasing-aaaahhh...~!" he moaned loudly into the empty bedroom.

~~~

A small tentacle slipped between his soaked lips and slid along his clit with barely any pressure.

Another on rubbed his thighs, teasing him more.

~~~

Nightmare's breathing stuttered as he moaned loudly, finally getting some relief from the ache. But the tendril was teasing. Barely putting any pressure on his clit but still enough to send sharp bolts of pleasure up his spine. The cold tendril moved up and down his slit while teasing the sensitive bundle of nerves at te top. The tendrils were teasing him and he hated it.

"Stop that!" he screamed in desperation. "Just get it over with already!"

~~~

A tentacle slid into Nightmare shallowly, barely penetrating him as one rubbed his clit slightly. The first tentacle withdrew after two thrusts and slid down Nightmare's leg.

~~~

Nightmare clenched his eyes shut when the tendril trusted inside and played with his clit. He moaned loudly when it slid out after a two thrust and slid down his leg causing him to shiver at the feeling of his juices trailing down.

Nightmare opened his eyed when a tendril poked his lips. He swallowed and opens his mouth, using a hand to guide the tendril into his mouth as he suckled at the tip with a soft moan.

~~~

The tentacle curled around his tongue loosely, smooth and slick with Nightmare's drool.

The tentacle on his lower leg trailed up again, dipping into his pussy briefly as another rubbed faint circles into his clit.

~~~

Nightmare hips began bucking slightly at the stimulation, begging for touch which only succeeded him grinding himself down on the large tentacle holding him.

The teasing the tendrils are doing drew out moans and and pleased hums from him, muffled by the tendril in his mouth.

~~~

A tentacle writhed between his ribs, dangerously close to touching his 'soul' and giving him some relief.

The tendril trailing his lips slid a few inches into him, stroking his inner walls before withdrawing again.

~~~

"Mmph-! Mm! Mnm." Nightmare moaned past the tentacle in his mouth as his eyes rolled back in pleasure. His hips now fully humping the tentacle as his mind blurred into a haze.

He pulls the tentacle out of his mouth with a gasp and panted. The tentacle kept poking his lips so he licked it, shivering and shuddering at the attention on his ribs and between his legs.

~~~

Cross frowned as he headed to Nightmare's room. He needed help with some paperwork. He had volunteered to do it because Nightmare hadn't been feeling up to it but now he had an urgent question.

He knocked on the door but received no answer. He opened the door slowly, freezing when he heard something akin to pain.

"Nightmare?" He asked worriedly, peeking into the room.

His whole face flushed brightly when he saw the predicament Nightmare had found himself in.

~~~

Nightmare heard the door creak open and looked over panting with need. His eyes widened and his face flushed when he saw Cross standing at the doorway but he's too far gone into his heat. His hips humping rhythmly on the tentacles as they teased him. His movements out of his control as he slowly gave into his heat. 

"Ah! Oh! N-no-! Ah~! P-please- don't-!" Nightmare gasped while arching his back, trying to get Cross to leave with his words of protests were being cut off by the teasing tendrils.

~~~

Cross' face was glowing now. Nightmare was in heat. He could smell it.

"Uh.. um..." He stammered. He felt embarrassingly hot, Nightmare's heat affecting him.

~~~

Nightmare struggled in his bonds but the tentacles held fast, not allowing him to move as they stimulated him more.

"Ah! Please! C-Cross...No-!" he protested but a tendril silenced him by gently sliding into his pussy. His protests were cut off with a loud pleasure filled moan. 

~~~

Cross took a deep breath. Nightmare needed help.

He walked over to Nightmare slowly. He knew how bad heat could be. He would help Nightmare.

~~~

Nightmare whimpered softly when Cross didn't leave.

"Just go! I don't want-! Aaah!" he cried out loudly when a tentacle rubbed his clit roughly and poked his lips again. Stars he's losing his mind. He can't let Cross see him like this. "Leave!"

~~~

Cross' eye lights glowed with determination as he climbed onto the bed, hovering over Nightmare. He silenced him with a kiss, rubbing his sternum gently.

~~~

Nightmare jolted in surprise at the kiss before he whimpered when a hand brushed his sternum. He turned his skull, tears in his eyes. "Stop!" he cried out. He hated being vulnerable. He hated this.

A tentacle shut him up by teasing his slit again, rubbing the hole firmly causing him to moan and buck his hips against his will. A tendril gently wraps around Nightmare skull and turns it back to face Cross, holding him in place. He choked on a sob, shaking his skull as he shuddered. He doesn't want this.

~~~

"Shh.... Everything's alright..." Cross tried to reassure him and caressed his cheek gently, giving him another kiss as his hand slowly trailed down the other's ribcage.

~~~

Nightmare cried into the kiss, closing his eyes tightly. He couldn't help but shiver as Cross trailed down his sensitive ribs, the tentacles stimulating him without a pause. His pussy throbbed painfully as more juices dripped down the tendril.

His legs which were beside Cross kicked out in a vain attempt to escape this hell of pain and pleasure but they were quickly seized by two tentacles, wrapping around his ankles firmly and spreading him wide causing him to squeak softly. With his legs spread the lips of his pussy parted making it easier for the tendril to rub his hole. He shivered with a strained noise of pain

~~~

Cross felt his dick summon and flushed slightly as he ground his clothed cock against Nightmare's wet entrance, using his hand to gently rub his spine.

~~~

Nightmare's breathing stuttered at the feeling but still struggled. The tendril between his legs realized Cross' intentions and moved away, letting the covered dick rub against Nightmare's pussy. The owner started to cry softly. His mind in a confused haze. He doesn't want this. But at the same time he craves the touch. It hurts and feels good at the same time. It's pain and pleasure. Hell and heaven.

Too much. He's so confused. He cries out softly, fighting against the tentacles. "Please...don't..."

~~~

Cross shushed him quietly and moved down to be facing Nightmare's dripping pussy. He licked his lips, intentions clear as he trailed his tongue over the other's clit.

~~~

Nightmare cried out loudly at the feeling of a warm tongue teasing his clit. It feels so different than the cold tentacles. It was warm. Wet and soft. Gentle and teasing yet firm. The touch was maddening, addicting. It's making him lose his mind. He hated it. He struggled harder, sobbing. "Please don't! Cross! Please-aaah! Stop! Ah...! Oh... Please-!"

~~~

Cross drew back a little to talk, using a finger to rub over Nightmare's clit gently.

"Shh..." He tried to calm him, rubbing one of the tentacles near him gently.

"Everything's okay..." He murmured softly.

~~~

Nightmare cried out with a sob as a finger rubbed his clit. Sharp bolts of pleasure shooting up his spine causing him to buck his hips.

The tendrils twitched, shivering at the touch and a small tentacles reached over to Nightmare's clit. They copied what Cross was doing drawing out a louder moan and a harder twitch of his hips. Two small tendrils reached over and parted the lips, exposing the dripping hole.

"Ah! No! Stop!" Nightmare pleaded. "Stop-hah! Aaahh~ Oh...! Please-Ah! Nohooooh." he sobbed as his struggles grew weaker.

~~~

"Stop." Cross hissed at the tentacles. He didn't want Nightmare to be too overwhelmed and they were a bit in the way.

~~~

The tendrils paused at Cross' command, twitching for a moment before moving away from Nightmare's pussy but still hovering near to give assistance. They just need the word.

Nightmare closes his eyes as tears dripped freely down his cheeks. His chest hitching with gasping sobs as he slowly relaxed when the sharp sensations stopped. He's still pretty much vulnerable to both his backstabbing tentacles and his friend Cross. It was embarrassing and humiliating. At least it stopped. He can feel his head again instead of that constant haze of pain and pleasure.

~~~

Cross' eye sockets widened. They were listening to him? He smirked slightly.

"Safe word is 'red'." Cross murmured quietly.

"Restrain him." He told the tentacles as he leaned down to plunge his tongue into Nightmare's tight pussy.

~~~

Nightmare' eyes widened in fear. What did he say?! 

"What?!" he screamed fearfully but it was too late when the tendrils obeyed Cross and pulls his arms above his head. His legs were spread open and he cried out loudly when Cross shoved his tongue inside. Because of his exposed position he couldn't move away, keeping him under their mercy.

"Aaah! Cross! Na-ah! Sta-aaahp!" he pleaded as he struggled but the tendrils kept him still, not letting him move away from the stimulation. He could feel something building up inside of him as he moaned and cried loudly. "Gah-aaah~!"

~~~

Cross thrusted inside of Nightmare gently but deeply and sucked on his lips slightly as he withdrew his tongue.

Nightmare tasted heavenly. He groaned quietly, sending the vibrations through the other's pussy and looked up, wanting to see how wrecked Nightmare already was.

~~~

Nightmare couldn't stop his hips from bucking, trying to reach Cross' mouth again, shuddering in pleasure when Cross sucked the lips of his pussy. He moaned loudly when vibrations spread through his sensitive cunt, threatening to make him come.

He panted as moan after moan escaped his open mouth with the occasional whimper. He feels so lost. He doesn't know what to do.

~~~

Cross caressed Nightmare's thigh gently as he continued to eat him out, trying to reassure him. He used his free hand to take the other's hand, intertwining their phalanges.

~~~

Nightmare shivered at the touch and grips the hand tightly, the tendrils loosened slightly to allow him the action.

He sobs as pleasure grew and grew. He doesn't know what it was. And it scared him. "C-Cross...s-something- ah!"

~~~

Cross rubbed Nightmare's thigh comfortingly, squeezing his hand slightly as he sped up slightly. He could feel that the other was close. Very close. Just a small bit...

~~~

Nightmare sobbed and writhed in pleasure that seemed to only increase. As if he's climbing towards an imaginary mountain and he's about to take a giant leap off of it.

He arched his back with a loud moan as pleasure shot through him. The tendrils massaged his ribs, back and spine, trying to ease him down from his high and calm him. One rubbed his skull as he panted softly, eyes blown out and hazy.

~~~

Cross lapped up his juices, intent on not wasting a single drop of it. He pulled back and swallowed, looking up at Nightmare. He was panting heavily and looked completely wrecked already.

Cross wiped his mouth on his jacket sleeve, smirking slightly. He had done that.

~~~

Nightmare shivered when he finally came down from his high, the soft touches sent bolts of soft pleasure through him. He looks up and saw Cross. He stares at him fearfully. What is he going to do?

Nightmare's trapped in his own tentacles. Clearly they listen to Cross and now him. He's weaker now because of his heat. Cross could do anything to him and he couldn't do a thing about it.

Somehow, the thought both scared him and aroused him.

~~~

Cross flushed slightly. Nightmare looked positively wrecked, if a bit scared. He caressed his cheek bone gently, squeezing his hand reassuringly.

"If you say the safe word I'll stop immediately." He reminded the other skeleton.

~~~

Nightmare leaned into the touch, seeking comfort and looks at Cross. The safe word, 'red'. All he has to do is say 'red' and he'll stop.

Nightmare gulped and nodded, putting his trust in Cross. "B-be gentle?"

~~~

"I will." Cross promised, giving his cheek bone a kiss as he removed his pants, still holding Nightmare's hand.

His cock was already leaking pre-cum, Nightmare's state having affected him severely.

~~~

Nightmare shivered at the sight and yelped when the tentacles moved to expose him more by raising his legs upwards slightly. He blushed brightly when his lips parted lewly, exposing his dripping hole.

He blushed and tried to curl but the binds kept him spread and exposed. He clenched his hand around Cross'. He's so fucked.

~~~

Cross took his cock into his hand and guided it to Nightmare's slick pussy, pushing inside slowly. He wiped his hand on the sheets and rubbed the underside of Nightmare's sternum gently.

He thrusted gently and shallowly, getting his cock inside inch by inch.

~~~

Nightmare gasped and groaned in pleasure as Cross sunk in deeper. He bit his tongue to try and contain the embarrassing noises that wanted to escape. But sharp bolts of pleasure shot up his cunt and spine with each inch Cross fed inside.

Nightmare panted and arched his back slightly to expose himself more to Cross, begging to be touched.

~~~

Cross gasped slightly as he was inside of Nightmare fully. He rubbed his ribs gently, staying still to let the other get used to the feeling.

He groaned quietly as the ecto-flesh around him toppled slightly, adjusting to his cock.

~~~

Nightmare moaned shakily as Cross sunk in deep, his insides shifting to accommodate the large intrusion. He struggled lightly.

"Please.. Move..." he groaned and bucked his hips, a tentacles poked at his lips which he suckled softly with a pleased hum.

~~~

"With pleasure~" Cross purred as he pulled out halfway, thrusting back into Nightmare remotely gently, trying not to snap and take the other roughly.

"Ahh~ so good..." He praised quietly, moaning slightly.

~~~

Nightmare moaned over the tentacle in his mouth as Cross thrusted inside. He huffed against the tentacle as his eye went fuzzy with pleasure. He clenched down repeatedly on Cross' cock, trying to give his mate as much pleasure as he can in his bound state.

~~~

Cross grunted in pleasure as Nightmare clenched on his dick. That felt amazing.

"Nng~" Cross moaned. "Please keep that u-upp..." He groaned. It felt so good... He thrusted inside Nightmare slightly harder, his control slipping.

~~~

Nightmare grunted and gently pulls the tentacle out to pant softly. He shivered when the force of the thrusts increased.

"I-I'll try." he says and clenched down onto Cross' dick. The effort was rewarded with a sharp bolt of pleasure.

~~~

Cross smiled and squeezed Nightmare's hand gently, showing that he appreciated it. He thrusted into him a bit harder, groaning when he was squeezed again.

"Nnnh~ so perfect~" He moaned softly, kissing Nightmare again.

~~~

Nightmare grunted into kiss before relaxing. Stars it's starting to feel so good.

His eyes snapped open in surprise and he moaned loudly. A small tentacle snuck between them and rubbed Nightmare's clit roughly.

~~~

Cross swallowed the moan easily, sliding his tongue over Nightmare's. He stroked his spine gently, thrusting inside the other with a moan.

He looked deeply into Nightmare's eye sockets, his eye lights slightly hazy.

~~~

Nightmare kept moaning and groaning and whimpering into Cross' mouth as more and more pleasure assaulted his small body. The pleasure getting higher and higher. His walls clenched hard onto Cross' dick as if it's trying to suck him deeper inside of him.

He met Cross' eyes with his own hazy eyes. The tentacles kept playing with his clit and helped Cross rub his spine causing him to buck his hips down onto the cock.

~~~

Cross moaned into Nightmare's mouth loudly when his dick was squeezed and he sped up slightly, the coil in his stomach area tightening. He was close already.

"You're do-doing so good..." Cross panted out as he separated their mouths for a few moments to catch his breath.

~~~

Nightmare shivered and moaned loudly at the praise, clenching much more excitedly after that. He began crying out loudly in pleasure.

"Please more! Fill me up! Fuck me!!!" he screamed and arched his back when Cross hit a special spot inside of him.

~~~

Cross panted loudly and aimed at that particular spot, speeding up. He was so damn close. Nightmare sounded so good.

"So close~ Go-gonna fill you~" He gasped, thrusting harder as he chased his orgasm.

~~~

"Ah! Yes! Please-! Aaah...! Fill me up! I want it! I want your cum!" Nightmare blushed at the words coming from his mouth but that embarrassment was chased away by Cross' thrusting. He's so close~! Almost there.

~~~

Cross sped up when he heard those words, panting heavily. Just a small bit...

"Nightmare... You're doing so well~" He moaned, thrusting deeper.

~~~

"Aaahaaaa~!" Nightmare cried out with tears of pleasure streaming down his face and came hard, his walls clenching onto the intrusion in a vice like grip. As if it's trying to squeeze the life out of it.

A tendril teased the base of Cross' cock to help the other reach his end.

~~~

"Nnnghhh~" Cross groaned as he was squeezed tightly. His whole body tensed up as he came hard, spurting his load deep inside Nightmare.

"Perfect..." He panted, his eye sockets droopy, his eye lights unfocused.

~~~

Nightmare panted and went limp in the tentacles' hold, his body twitching around Cross' dick from aftershocks.

The tentacles sensed that he's satisfied for now and gently released his limbs and massaged the sore bones. But his heat isn't over yet.

One tendril turned towards Cross and poked his cheek before pointing at Nightmare's blissful yet exhausted face.

~~~

Cross was ripped from his post-orgasmic haze when a tentacle poked his cheek bone. What did it want...?

Nightmare...?

He shrugged, kissing the other gently. He seemed satisfied for that time. Cross was going to stay and help him through his heat but they were both exhausted at that moment.

~~~

Nightmare leaned up to sluggishly kiss back, raising his arms to wrap around Cross weakly. He pulls away and nuzzled his cheek.

"Sleep. Stay?" he asks slowly and sleepily.

Before the skeleton could respond, a large tentacle pushed Cross forcefully to fall onto Nightmare's chest, clearly wanting him to do just that. They'll stay until Nightmare's heat is completely gone. Even if it means dragging another to help Nightmare get rid of it.

~~~

Cross let out a confused noise as he was pushed onto Nightmare. He was still inside of him. He slipped his dick outside and dispelled the magic, snuggling into the other skeleton. He kissed his cheek bone gently and cuddled into him softly.

"Course I will.." He mumbled quietly, hugging Nightmare.

~~~

Nightmare smiled and closes his eyes with a soft content sigh.

The tendrils gently moved them into a more comfortable position and wraps a blanket over them to keep them warm. They switched off the lights and curled around them, stroking their skulls and spine gently to rouse them to sleep.

Nightmare huffed with a pout at the tentacles but it was quickly wiped away as he yawned sleepily. He snuggled into Cross and closes his eyes, smiling slightly at the comforting touches.

~~~

Cross sighed softly and cuddled further into Nightmare, letting himself be moved without protest. He nuzzled the other's cheek bone gently, his eye sockets already closed. The comforting touches of the tentacles lulled him to sleep quickly.

**Author's Note:**

> Hope you liked it! Go check out xXUndertale_loverXx! They're amazing at writing! Recommended! Anyways, thanks for reading!


End file.
